This invention relates to circuit breakers, and, more particularly, to a trip system for a high-level interruption of current that functions as a result of the rotor system of a rotary circuit breaker.
Override systems of the prior art typically use electronic trip units to respond to high-level fault conditions and initiate the separation of all of the contacts in a plurality of rotary circuit poles ganged together to form a multi-pole circuit breaker. For example, in U.S. Pat. No. 4,616,198 entitled xe2x80x9cContact Arrangement for a Current Limiting Circuit Breakerxe2x80x9d, separate electrodynamic forces may be generated in any of the poles of the circuit breaker causing the contact arms to pivot upon an overcurrent condition. As the contact arms are pivoted, the contacts secured to the arms are separated from the stationary contacts mounted within the circuit breaker, thereby stopping the flow of electric current through the contacts. In that invention, a contact arm associated with one pole of the circuit breaker can open independently of the contact arms associated with the other poles of the circuit breaker. Therefore, the current in only one pole is interrupted upon an overcurrent condition. The override system serves to avoid the occurrence of such xe2x80x9csingle phasingxe2x80x9d, where one of the phases interrupts independently of the remaining phases.
Another use of electronic trip units is recited in U.S. Pat. No. 4,672,501 entitled xe2x80x9cCircuit Breaker and Protective Relay Unitxe2x80x9d, which describes the use of electronic circuitry to determine the occurrence of an overcurrent and the use of a current transformer to sense circuit current. However, when using such circuitry in conjunction with rotary contact arrangements, the current transformer cores can become saturated upon occurrence of a short circuit overcurrent and an auxiliary trip unit must be employed to ensure short circuit overcurrent protection.
Short circuit overcurrent protection in rotary contact circuit breakers is also described in U.S. Pat. No. 5,103,198 entitled xe2x80x9cInstantaneous Trip Device of a Circuit Breakerxe2x80x9d, wherein the overpressure developed within a circuit breaker arc chamber upon contact separation in one pole drives a piston against an operating mechanism trip bar to actuate contact separation in the remaining circuit breaker poles. However, it has since been determined that the overpressure response is sensitive to voltage levels upon arc occurrence and that it is less sensitive to short circuit current values.
Electronic methods of contact separation, especially those that operate as the result of magnetic repulsive forces, are slower to respond and thereby increase the time required for a circuit breaker operating mechanism to respond to an overcurrent.
In the present invention, a circuit breaker assembly includes first and second rotary contact assemblies mountable to a base member, a circuit breaker operating mechanism mounted to the first rotary contact assembly, and a trip bar in mechanical communication with the first rotary contact assembly and the circuit breaker operating mechanism. The rotary contact assemblies each include rotors rotatable about axes therethrough and movable contact arms pivotally mounted within the rotors. The circuit breaker operating mechanism serves to position the rotors to separate movable contacts thereon from fixed contacts. A trip override device includes spring links operably connected via springs to each of the rotors of the rotary contact assemblies and the trip bar. The trip bar comprises a trip rod having trip levers protruding radially therefrom and being in mechanical communication with the rotary contact assemblies.
The above trip override system allows contact separation in one pole to actuate the operating mechanism in all other poles in the circuit breaker. The system has many advantages over the prior art, including that it functions independently of the system voltage by working off the mechanics of the rotor system.